Discharged 12V Battery

Short version: Any experience(s) with “jump-starting,” or charging, a Gen-2 with a discharged 12V battery? I haven’t started researching this question in the owner’s manual yet, but I will shortly.

Longer version:

Since we got our Prius Prime in mid-May, I haven’t driven our 2009, and in fact I de-insured it waiting for my wife to get her Learner’s Permit. She’ll be beginning to learn driving with it in January.

Anyway!

Looks like I let the 12V battery discharge. I tried to keep starting it up once in a while, but got super-busy at work and... That battery has been replaced once since late 2008 when we bought it, so the battery itself probably hasn’t failed; just discharged.

I don’t know the state of the traction battery. Fair chance it’s discharged too, but don’t know.

I have a Prius Prime, which has a pretty-much-regular car battery, to jump-start (in some sense of the word!) from, and I also have an ordinary-lead-acid-battery charger (no idea whether that could be usable).

I gather that the Gen-2’s 12V battery is somewhat like a flashlight, “dry cell” battery — very different from traditional car batteries, so iffy as to whether that charger could be useful.


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FWIW, that’s how the service advisor at the dealer described it when they changed it out … 3ish years ago.

OK, great information, thanks! As I recall, the Prius design does include a more-or-less traditional starter motor, powered from the 12V battery, although it obviously doesn’t normally use it. So charging it up should conceptually be sufficient to restart the whole system.

The traction battery normally charges the 12V battery, at least during normal operation, like the alternator on traditional car. I imagine it doesn’t when the hybrid system is turned off, but if it does, then presumably the traction battery is discharged too.


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So, it was a long time ago, but I recall reading in the owner’s manual that it does include a means of starting the engine from the 12V battery alone, in the event that the traction battery gets completely discharged. As I recall, they made it sound like a traditional starter motor, which of course it would never use normally, but perhaps it’s actually just a means of driving MG1 from the 12V.

When I get a chance to read again in the owner’s manual, probably later today, I’ll quote it here, if I find it...


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OK. I’ll let you folks know how it goes then!

 

Yes.


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I was not able to find what I remembered seeing in the owner’s manual about having a some sort of a traditional starter motor powered from the 12V in the event that traction battery discharges. Then again, I didn’t look very hard, because I did find several statements that, if the traction battery discharges, you can’t start it, as you pointed out.

So, no idea where I read (i.e., misread) that from... Again, it was ... like 9 years ago.

Anyway, I attempted to jump-start it from our Prius Prime (again, it has a traditional 12V battery). Not clear why, but that didn’t work at all: Hooking it up to the P.Prime’s 12V had no effect whatsoever.

So, I pulled out my 12V battery charger, and changed it from 12V/10A to 12V/2A, and hooked it in. Thankfully, the ammeter immediately showed that it was drawing current. I first tried to power it up after 15ish minutes charging, but that clearly wasn’t enough. So I plugged it in for ... an hour or so, and then was able to start it up. The traction battery was still fine.

I then drove it around for 10ish minutes or so, and brought it back home. When I shut it off, the water-pump grind (powered by the 12V battery) sounded pretty anemic, so I started it up again, and drove it around for another 15ish minutes or so, and it seems fine now.

I’ll probably check that it still powers up fine tomorrow, basically to make sure the 12V battery has at least that much retention. That is, see whether it was damaged by discharging. Probably not, but we’ll see.


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Not likely I was thinking of another car, but perhaps what I read it from was thinking of another car.

Or maybe I’m just an old geezer (56) and fantasized the whole thing!


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I remember it sticking in my mind though, because I wasn’t expecting it to have such a provision.

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OK, yes, that’s a reasonable point. I probably only charged it up to where it can function, but not full.

Still, it’s a pretty small battery, right? Do any of you know right off approximately how big it is, in Amp-hours, compared to Traditional car battery?


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